Conventional electronic expansion valve makes use of the principle of a step-motor, in which a magnetic rotor member is driven by a coil to rotate in a forward direction and a reversed direction and a rotation movement of the magnetic rotor member is transformed into an up-and-down movement of a screw rod. A valve needle which is connected to and driven by the screw rod moves up and down to control the amount of flow of the electronic expansion valve.
In the prior art, a stop rod, a slip ring and a spring rail are all arranged outside the magnetic rotor and thus the electronic expansion valve is bulky. Besides, the magnetic rotor and the screw rod are fixedly connected together by injection molding. In use, two technical solutions are typically adopted: i) the magnet moves with the screw rod; however, the relative position between the magnet and the coil will change during the movement, thereby having an influence on the full play of the magnetic performance; ii) an axial movement limiting mechanism is additionally provided for the magnet, therefore the magnet rotor will subject to two forces simultaneously, i.e. a downward spring pushing force for positioning which is generated by a positioning spring and a downward axial force transmitted from the valve needle by the screw rod; as a result, the friction resistance against the magnetic rotor becomes large, the magnetic rotor becomes deteriorated in flexibility and tends to be jammed. In addition, the demand on the accuracy of coaxiality is increased during manufacturing of the magnetic rotor.
Japan patent publication No. JP2006348962 discloses an electronic expansion valve in which the stop rod, the slip ring and the spring rail, etc are arranged inside the magnetic rotor. However, the electronic expansion valve has the following disadvantages. Since the magnetic rotor and the screw rod are fixedly connected in an axial direction so that the magnetic rotor still subjects to a downward axial force transmitted from the valve needle by the screw rod, the magnetic rotor is poor in flexibility. Furthermore, since the stop rod is integrally formed with the magnetic rotor by injection molding, magnetic powder on the magnetic rotor will easily drop off during the course of stopping moving, and the matching margin between the stop rod and the slip ring is small. In addition, since the slip ring and the spring rail are mounted at the cylindrical portion protruding from a valve seat which is formed by stretching process, it is very difficult to guarantee the coaxiality of the cylindrical portion protruding from the valve seat. Besides, the core of valve seat consumes too much material and tends to make noise.